by Heidi Norman
When it enters the sea, dust can make a big difference. The iron that makes our deserts red is a potent fertiliser for plankton, the primary producers in the ocean. Red Dawn wasn’t studied as a fertilising event, but dramatic dust storms in 2002–3 were linked to a drop in carbon dioxide in the atmosphere, which was attributed to plankton taking in more carbon because they were photosynthesising more. So, farmers who flog their paddocks help the fish in the sea by helping the algae that sustain marine life. Some scientists have warned that to plant millions of trees to reduce carbon dioxide could backfire if there is less dust from degraded lands reaching the sea, although that conclusion has been disputed. Australian dust is first-class fertiliser, with 50 per cent more iron than the global average.
Dust comes and goes everywhere. Dust from the Lake Eyre basin – Australia’s dust hotspot – is thought to reach the Philippines, Antarctica and Patagonia, carried on the prevailing winds. It may well be fertilising Borneo rainforests, just as Saharan dust fertilises the Amazon, and central Asian topsoil enriches Hawaii. Like the internet, dust connects the world. New Zealand receives so much dust from Australia – up to 200 000 tonnes in a single event – that Australians go there to study it. Scientists can tell where in Australia the dust comes from by testing which of 25 trace elements it contains; some grains found on Fox Glacier were traced back to Wilcannia in western NSW. Before reaching New Zealand, Australia’s dust grains dance past the smokestacks of coal-fired power stations and mines, acquiring pollutants such as lead, nickel, copper and zinc, which show up on New Zealand glaciers at high enough levels to cause concern. Smoke from bushfires journeys across as well, and spores of wheat rust, a feared disease that ravages whole crops.
Dust is rich in information. Places in which it accrues are archives, able to inform us about past climates (ice ages are super dusty), past wind directions and past activities. In a peat mire in Kosciuszko National Park, some of the lead in the dust can be traced to the first mines at Broken Hill in the 19th century and to Australia’s first leaded fuel in the 1930s. Industrial arsenic, zinc, copper and cadmium are also stored in that remote alpine site. The mire shows that Australia became much dustier after 1869 as farmers opened up the land and rabbits chewed it bare, to reach an acme during the Federation Drought. There was so much topsoil in transit then that, to quote one observer, ‘Every fence, at some point or other, was so far buried that stock could go from paddock to paddock.’ One pastoralist wrote about ‘three parts of this country blown further east’. Australia today is less dusty, because many of the grains that could blow away have done so, and because many landholders have embraced Landcare and the National Soil Conservation Program.
The dust that settles in our homes is a bit of everything. There are mineral particles from soil and buildings, fibres from wood and paper, fragments of foam rubber and plastic, paint flakes, food particles, soot from cooking, the droppings of cockroaches and silverfish, pet dander, human excretions and secretions, and other organic debris such as the desiccated moth our shoe may have crushed into the carpet. Near open windows there are more grains of sand, leaf particles and pollen, while the soft grey dust under the bed is less diverse and dominated by shed skin and textile fibres. The ingredients of most importance to humans include mite droppings, pollen and lead.
The animals that dominate our dust are tiny mites. Hordes of mite species find their way into homes to live in flour and other dried foods, on pets, mice and pot plants. Of the true dust specialists one home rarely has more than ten species, with as many as five in a carpet, one of which is apt to dominate. The world’s most successful dust dweller, likely to be in your bed and mine, is a minuscule mite with a very long name, Dermatophagoides pteronyssinus.
Fodder for dust mites includes the flakes of bacteria-laden skin we constantly shed, along with pollen grains, fungi and plant fibres. They do especially well on the dried semen found on sheets, a rich source of protein and sugars. In our beds they do best at the warm foot end and worst in the hot central zone our bodies occupy. They prefer the sheet and blanket above us to the quilt or bottom sheet. They like buttons and seams. They burrow up to two centimetres into foam mattresses which, by holding moisture, suit them better than mattresses with springs. The air turbulence we create when we slide into bed, and the thermals generated by our heat, ensure we inhale mite droppings left on our sheets.
Dust mites lurk in carpets, sofas, curtains and even mould on walls. They can crawl only a few centimetres a minute, but they are adept at hitchhiking. When some dyed mites were released onto a sofa they soon appeared in other rooms and within ten days were in the family car. So when we visit friends, mites on clothes are part of our entourage. A cardigan can carry well over 200. Dust mites turn up in Antarctic field stations and even in the Mir Space Station.
Being barely a third of a millimetre long, these mites come to our notice only if they make us wheeze. They are the main cause of asthma, the most common chronic disease among Australian children and a problem for many adults. Because dust mites are less than efficient at digestion, their droppings are rich in digestive enzymes, which are so chemically active that many people, including me, suffer allergic reactions.
Other components of dust that can irk our airways include fungal spores, flakes of skin shed by pets, and pollen. Grasses, sheoaks and other plants that rely on the wind to shift their pollen release prodigious amounts. Around the world, pollen and mite allergies are increasing. The favoured explanation is the hygiene hypothesis, which posits that our cities and homes are so clean that we imbibe too few microbes to keep our immune systems active enough to prevent exaggerated responses such as allergies. Children and adults alike need exposure to the microbe-rich dirt of rural or natural landscapes.
The good news about dust is that one constituent is not the problem it was. Australian homes now harbour less lead, thanks to a phase-out of lead-based paints in the 1970s and leaded petrol by 2002. Now that our fuels are lead-free, the main concerns are with the ultra-fine particles that bypass the filtering systems in our airways to contribute to fatal heart and respiratory diseases. Red Dawn was rich in ultra-fines, but in cities, by a large margin, cars are the main source. A study on rats showed that when these particles are inhaled some of them reach the brain, where, in sufficient numbers, they probably do great harm.
An emphasis on all that is bad about dust does it a disservice. Without dust there would be more carbon heating up the atmosphere, fewer fish in the sea, less soil on some valley floors and, importantly, next to no rain – because raindrops need particles to form on. Mineral dust and soot from bushfires, floating thousands of metres above Australia, make summer downpours possible.
Scientists are excited by growing evidence that live bacteria and fungi in the troposphere, and perhaps algae and pollen as well, act as nuclei for rain. More than 2600 species of bacteria were found in air that reached North America from China. Penicillium mould has been detected 77 kilometres above the ground. The sky is very alive. Hundreds of thousands of microbes can exist and breed in a cubic metre of air, although their numbers drop off with altitude. Bacteria have been found in the centre of hailstones. Scientists have proposed that by increasing cloud ice, bacteria even contribute to thunderstorm form and lightning ferocity.
The story of dust is ultimately the story of everything, because the world is made of and influenced by dust. Our planet formed from coalescing dust and gas, so that as children of the Earth we are all made of dust. Cosmologists look to extraterrestrial dust for insights into the universe. The Curiosity Rover was sent by NASA to Mars to see if Martian dust would disclose proof of past life. Stardust was a space probe that collected dust from comet Wild 2 in the hope that comets preserve primordial dust from early in the life of the universe.
Our world reveals itself as a very different place when, in all its forms, dust becomes the focus. Dust reveals the power of tiny things to harm us, help us, shape our world and teach us about ourselves. Red Dawn forced mill
ions of Australians to grapple with the stuff, but we shouldn’t need a colossal storm to remind us that dust is important.
Love bug
Messages from Mungo
Germ war breakthrough
Copulate to populate:
Ancient Scottish fish did it sideways
John Long
The intimate act of copulation is old – very old. In fact, it first evolved in ancient armoured placoderm fishes called antiarchs 385 million years ago.
Fossils of the antiarch Microbrachius dicki show males with large bony L-shaped claspers for transferring sperm, whereas females bore small paired bones to help dock the male organs into position.
These discoveries, published in the journal Nature, represent the first appearance of sex involving copulation in vertebrates. It’s also the first time in vertebrate evolution that males and females appear with distinct differences in their physical appearance.
Little arms, big genitals
Microbrachius means ‘little arms’, a reference to its small paired pectoral limbs. It inhabited ancient rivers and lakes about 385 million years ago. Its species name dicki honours Robert Dick, an avid fossil collector in the late 19th century who first found its fossils in the north of Scotland.
The new discoveries began late last year when I was working at the University of Technology in Tallinn, Estonia, with my colleague Elga Mark-Kurik. She handed me a box of isolated Microbrachius bones from Estonia to examine. I found a tiny plate, less than 2 centimetres long, which had a tube of bone attached to it that I couldn’t identify.
Eventually I realised it was a clasper – a primitive vertebrate sexual organ. Claspers are found in male sharks and rays and used for copulation. It was one of those sublime eureka moments: it basically meant a complete rethinking of the evolution of sexual strategies in jawed vertebrates.
Antiarchs had never before shown any evidence for this type of reproduction. We had long assumed they simply spawned in water, like many living fishes. The new discovery meant they had the ability to copulate and therefore internally fertilise their eggs. As antiarchs are the most primitive jawed vertebrates, it meant that highly complex sexual reproduction first appeared at more or less the same time as jaws and paired hind limbs appeared.
We began searching other museum collections in Europe, Australia and the US for more evidence. Eventually some amazing complete specimens of Microbrachius held in private collections by UK and Dutch collectors were revealed to us, showing distinct male and female features. These were then donated to the Natural History Museum, London, so we could complete our study.
First vertebrates copulated ‘square-dance’ style
It’s bizarre that these tiny fishes mated from a sideways position, the male and female resting alongside each other. They likely intertwined their bony jointed pectoral appendages (arms) using the rows of hooks on their inside edge. The outside arms could have helped them manoeuvre their large claspers into the mating position. With their hooked ‘arms’ interlocked, the act of copulation in these fishes somewhat resembled square dancing the do-si-do.
The female’s paired genital plates bore a roughened surface, a bit like a cheese grater, for the male claspers to latch on to. Once the male’s clasper was in the mating position only the tip could be inserted inside the cloaca of the female to deposit sperm.
Despite their awkward looks, Microbrachius were highly successful little fishes whose species are found in the UK, China and Estonia. The antiarchs could have all mated in this way, as other forms such as Bothriolepis show similar genital structures preserved.
Bothriolepis was the most ubiquitous vertebrate known in the Devonian period, with more than 150 species found. It lived on every continent, including Antarctica. Such antiarchs were probably the world’s first truly widespread vertebrates. We now think it likely that their movable bony arms, which facilitated copulation, were the key to their migratory success.
Placoderm sex and live birth
The new discovery follows on the heels of a string of recent finds elucidating how the oldest backboned animals mated. In 2008 we discovered the oldest evidence for live birth in a placoderm fish fossil from Gogo, Western Australia.
It showed a 3D embryo fossil attached by a mineralised umbilical cord. We named it Materpiscis attenboroughi, meaning ‘Attenborough’s mother fish’.
This discovery was followed in 2009 by another equally unexpected find, more placoderm embryos inside another group of placoderms, the ‘arthrodires’.
The arthrodires were the most diverse clade of placoderms. Yet despite thousands of specimens in museum collections, none had shown any evidence for how they reproduced. Our discovery proved they used internal fertilisation and that males had bony claspers for mating.
In early 2014 we added to this by showing that placoderm claspers did not develop in the same way as shark claspers, as part of the pelvic fin, but evolved more or less like an extra pair of limbs.
Placoderm claspers were at first fixed rigidly to their body plates as in Microbrachius, so the fish had to move its entire body around to mate. More advanced placoderms such as the arthrodire Incisoscutum – a group of armoured jawed fishes – evolved flexible bony claspers capable of rotating forwards and becoming erect for mating.
The rise and fall and rise again of male intromittent organs
Our new research implies something that was thought impossible in biology – that fishes went from using copulation (internal fertilisation) to reverting back to external fertilisation (spawning in water), the default primitive condition seen in jawless fishes such as lampreys.
This must have occurred when bony fishes first evolved from placoderms, as none of the primitive fossil or living species such as Polypterus show any evidence for internal fertilisation.
We know that coelacanths mate using internal fertilisation, even though they lack copulatory structures. Some families of advanced bony fishes, the teleosts, evolved different kinds of internal fertilisation. Guppies, for example, use a modified anal fin spine to transfer sperm, although none of these teleosts ever developed paired claspers similar to those in placoderms or sharks.
Our study concludes that the most primitive jawed vertebrates originally evolved copulation as the main way of mating then lost it early on in their evolution. Later it reappeared again and again in many different animal groups.
Snakes and some lizards have paired penises but crocodiles, tortoises, mammals and some birds all have a single penis. The Argentine Lake Duck has the longest penis relative to body size for any living vertebrate (43 centimetres for an average-sized duck). The penis was secondarily lost in many lineages of flying birds.
We humans thus mate in a way that first evolved in crocodiles and tortoises back in the age of dinosaurs. We can thank our distant ancestors, the placoderms, for first evolving this unique method of reproduction.
Love bug
Messages from Mungo
The mind of Michio Kaku
Tim Dean
Michio Kaku has an extraordinary mind. It loves nothing better than occupying itself untangling the mathematics of subatomic strings vibrating in 11 dimensions. ‘My wife always thinks something strange is happening because I stare out the window for hours,’ he says. ‘That’s all I’m doing. I’m playing with equations in my head.’ In his day job, Kaku works at the very fringes of physics. He made a name for himself as co-founder of string field theory, which seeks to complete Einstein’s unfinished business by unifying all the fundamental forces of the universe into a single grand equation. He regales the public with tales of multiverses, hyperspace and visions of a better future built by science.
Hyperbole is part of his style. He once urged humanity to consider escaping our universe, which several billions of years from now will be in its last throes, by slipping through a wormhole. Hardly a pressing concern for today, but such proclamations lasso attention and get people to think big.
Kaku certainly thinks big in his latest book,
and there’s plenty of hyperbole. But The Future of the Mind is somewhat of a surprise. What is a theoretical physicist doing writing a book about the mind – a topic usually reserved for neuroscientists, psychologists and philosophers? As a philosopher myself I was curious to see if a physicist could shed some photons on the problem. I took the opportunity when he was in Sydney spruiking his new book to find out.
Kaku is short in stature but his personality fills the room. Eyes are drawn to the sharp-suited figure with the shock of white hair, and that melodic voice filled with earnest urgency. It’s hard to resist the limitless passion for wonder. Sitting with him in a corner of the Pullman Hotel across from the green expanse of Hyde Park, I ask him what drew him to write about the mind.
‘There are two great mysteries that overshadow all other mysteries in science,’ he starts, slipping into his signature avuncular lecturer’s tone. ‘One is the origin of the universe. That’s my day job. However, there is also the other great mystery of inner space. And that is what sits on your shoulders, which believe it or not, is the most complex object in the known universe. But the brain only uses 20 watts of power. It would require a nuclear power plant to energise a computer the size of a city block to mimic your brain, and your brain does it with just 20 watts. So if someone calls you a dim bulb, that’s a compliment.’
I’m not convinced Kaku has ever been compared to a low wattage bulb. However, I’m immediately struck by how firmly he sees the mind through the lens of the physical. This places him squarely on one side of a centuries-old debate about the nature of the mind. In one corner are those who assert that the mind is nothing more than physical processes – electrical impulses cascading throughout the brain. In the other corner are those who hold that the mind is something above and beyond the physical – that it is made of stuff not found on any periodic table, with properties that can’t be described in physical terms. It’s a debate close to my heart – my honours thesis grappled with the possibility that the mind can be explained in physical terms alone. Kaku, it seems, thinks it can.
